Conceptual Arguments for Testing

Testing and Agile
- Notion of a ‘release’ is gone
- Notion of a ‘spec’ is gone
- Cycles are much faster
- Automation becomes a requirement
Testing and Design
- Insight (not shared by all) that TDD supports design
- Insist on looking at the class/module/unit first as a black box that delivers services
- Good design delays all decisions that can be delayed until further requirements are nailed down.
- Refactoring is how new requirements are incorporated
- Good test suites is what gives you the confidence to refactor
Testing and Refactoring:
- Recall: Refactoring is a controlled technique for improving the design of an existing code base. Its essence is applying a series of small behavior-preserving transformations, each of which ‘too small to be worth doing’
- So you always should have solid tests before you start refactoring
- Each small change is verified to not have changed behavior

Fundamental motivation for testing: reduce costs
- Writing tests should over the lifetime of the code cost less
- Otherwise it’s not worth doing
- How does it reduce costs?
Breaking it down: Why Test?
- Finding bugs early
- Reducing errors
- Making assumptions explicit - documenting code with code [how do test do that?]
- Make refactoring possible and safe [how safe?]
- Driving design decisions (TDD?)
- Discover bad design decisions [how?]
Philosophy of Commenting
- Believe or not, it’s controversial
- Comments should not duplicate what the code clearly says
- Of course, “clearly says” is in the eyes of the beholder
- One philosophy: If you feel the need to put in a block comment, extract that section into a method with an intention revealing name